100 pushups

Just combine them all into 1 activity and use the total time for all of them (including rest bet sets) minus time spent resting between exercises. However, I wouldn't count any time doing a wall-sit because you really aren't burning many if any cals doing that.

You can choose any "cardio" activity you like for this (strength or calisthenics, for example) but enter a cal # that best fits your metabolism and activity level; ie, don't rely on the # MFP defaults to for the category because it's likely to be too high.

For example, I do a 5x20 pushup,5x10 pullup and 5x15 dip routine 3x's a week and use the Strength Category at 120 cal/hr to calc cals burned for this purpose.

I just use the total time doing this routine, including the rest time bet sets (3.5 mins) but minus rest time bet exercises (15 mins) which usually works out to a 55-60 min (110-120 cal) routine for me.

I have been able to maintain my weight consistently over the past 4 months recording this routine in this way, so it works for me. If it wasn't right, I'd expect to gain or lose weight over time as a result of over or under eating based on the calculation.